Borderline serous tumour of the testis and paratestis is an uncommon entity. We report a case of borderline serous tumour of a 59-year-old male, who presented with a right testicular swelling which was clinically suspicious of carcinoma. Radical orchidectomy was performed and a cystic lesion was identified in the testis. Macroscopically the tumour was composed of a unilocular cyst with excrescences in the inner surface. The histological features were identical to the ovarian counterpart of borderline serous papillary tumour. The excrescences were formed by stratified columnar epithelium, which exhibited mild nuclear pleomorphism and mitotic activity, with a fibrovascular core and scattered psammoma bodies. There was no lymphovascular or stromal invasion. The lesion was surrounded by a dense fibrous wall. On immunohistochemistry, the lining epithelial cells expressed cytokeratin AE1/AE3 but not carcinoembryonic antigen or calretinin. Following the removal of the tumour, the patient was followed up and no recurrence or metastasis has occurred to date. This case highlights the need for clinicians and pathologists to be aware of this rare entity and to develop the best approach for patient management.
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